Introduction on How Structured Light Works

Hi, my name is Trevor Dowd. I work in the DLP Advanced Light Control group at Texas Instruments. This is a multi-part series on creating an industrial 3D machine vision system using DLP technology.
Today, we're going to discuss the most common 3D machine vision techniques, including structured light, the technique used by DLP. We'll also learn about DLP resources, including chipsets, TI designs, and the DLP design network partners.
First, let's take a look at how structured light works inside 3D machine vision. In 3D machine vision, depth is calculated using triangulation. An identified feature is matched between two different viewpoints in space and optical pixel ray vectors are matched from pixels between the two different viewpoints.
In a structured light application, one of those viewpoints is a projector and another is a camera. The projector projects light onto the object and that light is captured by the camera. The camera is able to identify all of the points that both the projector and the camera can see.
Two different chipset types available from DLP products are advanced light control chipsets and Pico video and data display chipsets. In advanced light control chipsets, they're meant for machine and industrial applications like 3D machine vision. They're capable of high speed pattern rates, up to 32 kilohertz on some chipsets. They're capable of pixel accuracy, meaning that the image that you load in is displayed one to one with the image that comes out of the projector. And they have triggering ability.
In Pico video and data display chipsets, they're meant for display applications, meant to be seen by the human eye. They're capable of normal video rates, like 60 hertz or 120 hertz, and they have some video processing algorithms to optimize display appearance.
Two things to consider when designing your 3D machine vision system are speed and resolution. Here are DLP advanced light control chipsets, broken down by resolution in pixels and maximum bandwidth in gigabits per second. When you design your system, you need to take into account what resolution DMD you need in order to get the resolution of the point cloud that you desire. Also, you need to get the speed of the DMD to match the speed of your camera. The most commonly used DLP chipsets for 3D machine vision are the DLP3000, the DLP4500, and the DLP6500.
Another factor to consider when designing your system is the operating mode. Now, operating modes differ between DLP chipsets. But typically, there's a video mode, which is not recommended for industrial applications due to the display algorithms for optimized appearance, similar to Pico video and data display chipsets. So we're not going to talk about that one today.
Video pattern mode is available on some chipsets, which is a pixel accurate mode, meaning that the images are displayed one to one with the data that is loaded in. They have unlimited amounts of data which can be streamed over parallel RGB ports, like HDMI or display ports. And they also support normal video rates, up to 120 hertz.
There's also pre-stored pattern modes, which is stored in the flash or the DRAM of your device. This mode is also pixel accurate, and it has limited amounts of memory to store patterns. So pre-load patterns, which can be 8-bit or 1-bit patterns into the flash or DRAM, and then stream that through the controller to the DMD, or Digital Micromirror Device. Maximum pattern rates are available in the pre-stored pattern modes.

Description

July 18, 2016

Key information on how DLP structure light works is provided in this section, including: